CMB2001/L06 Transcriptional Responses to Stress & Infection II

Question 1

What is the role of E3 Ubiquitin ligase?

Answer 1

Facilitates the attachment of ubiquitin chains to target proteins

Question 2

Define hypoxia.

Answer 2

Lowering of the oxygen concentrations compared to sea level +-20.9% oxygen

Question 3

Give 3 physiological processes that require a hypoxia response.

Answer 3

Placenta development
Heart
Bone
Vasculature development

Question 4

What does hypoxia response allow adaptation to? (2)

Answer 4

High altitude living
Intense muscle exercise

Question 5

Give 3 cellular responses to hypoxia.

Answer 5

Restoration of oxygen homeostasis
Cell survival
Cell death

Question 6

What is the HIF system?

Answer 6

Hypoxia Inducible Factor
Heterodimeric transcription factor HIF-a and HIF-1B

Question 7

Where is HIF-1a expressed?

Answer 7

Ubiquitously in all tissues

Question 8

Where is HIF-2a expressed?

Answer 8

Restricted to certain tissues

Question 9

Where is HIF-3a expressed?

Answer 9

Restricted to certain tissues
Lacks C-terminus transactivation domain

Question 10

How does HIF-3a function?

Answer 10

As a dominant negative inhibitor for HIF-1a and HIF-2a
Has been shown to activate a different set of genes in hypoxia

Question 11

What do Proline Hydroxylases (PHDs) require to function?

Answer 11

Oxygen

Question 12

How is HIF-1a regulated?

Answer 12

Transcription
Translation - evades block
Post-translational regulation - lack of oxygen inactivates PHD proteins

Question 13

Describe canonical regulation of HIF (in normoxia).

Answer 13

Oxygen sensing
Ubiquitination and degradation
Stabilisation in hypoxia
Dimerisation with HIF-1B
Transcriptional activation
Target genes

Question 14

In what form can asparagine interact with target gene mRNA?

Answer 14

Unhydroxylated

Question 15

Name 3 pathways controlled by HIF.

Answer 15

Oxygen supply
Transcription
Cellular metabolism
Cell growth
HIF control
Cell death

Question 16

How does hypoxia aid cancer? (3)

Answer 16

Activation of HIF stimulates angiogenesis to bring oxygen and nutrients to tumour
Regulates other tumour characteristics: evasion and metastasis
Enhanced growth and survival and increased glycolysis

Question 17

Describe the structure of p53.

Answer 17

Typical for transcription factors
Distinct DNA binding and multimerisation domains
Transactivation domain (TAD)
P - proline-rich domain
NLS- nuclear localisation sequence
Tet - tetramerisation domain

Question 18

Give 3 positive roles of p53.

Answer 18

Tumour suppression
Stem cell modulation
Development
Fertility

Question 19

Give 3 unfavourable roles of p53.

Answer 19

Ischemia
Treacher Collins syndrome
Neurodegeneration
Aging

Question 20

What is the role of ARF?

Answer 20

p14^ARF - tumour suppressor
Disrupts interaction between p53 and Mdm2
Increases levels of transcriptionally active p53

Question 21

When is p14^ARF expression induced?

Answer 21

As a result of increased cellular proliferation

Question 22

What is the role of Mdm2? (3)

Answer 22

E3 ubiquitin ligase
Promote ubiquitination of p53 for degradation by proteasome
Keeps p53 levels low in undamaged cells

Question 23

Describe how Mdm2 inhibits p53.

Answer 23

DNA damage causes phosphorylation of p53 at Ser15 by ARM or ATR kinases
Mdm2 phosphorylated
Disrupts interaction between p53 and Mdm2

Question 24

Describe the Mdm2 feedback loop.

Answer 24

p53 stimulates Mdm2 expression
Negative feedback loop limiting extent of p53 activation

Question 25

Give an example of negative feedback among transcription factor pathways.

Answer 25

p53 induces its inhibitor Mdm2 causing its proteolytic degradation HIF1a induces PHD proteins that cause its proteolytic degradation NF-kB induces its inhibitor IkBa that removes it from nucleus and retains it in cytoplasm

Question 26

Explain how cancer cells inhibit p53.

Answer 26

Mutation causes loss of ARF/ATM function Mdm2 amplification Viral infection of E6 Mutation or defects with p53 Arrests apoptosis

Question 27

What is Li-Fraumeni Syndrome?

Answer 27

Hereditary cancer disposition syndrome Most commonly caused by mutation in gene TP53 for p53

Question 28

How do the NF-kB and HIF pathways differ?

Answer 28

NF-kB activation involves degradation of an inhibitor (IkBa) HIF and p53 are degraded continuously in unstimulated cells and become stabilised upon exposure to activating stimulus